Wedelolactone, a plant coumestan, was shown to act as anti-cancer agent for breast and prostate carcinomas in vitro and in vivo targeting multiple cellular proteins including androgen receptors, 5-lipoxygenase and topoisomerase IIα. It is cytotoxic to breast, prostate, pituitary and myeloma cancer cell lines in vitro at μM concentrations. In this study, however, a novel biological activity of nM dose of wedelolactone was demonstrated. Wedelolactone acts as agonist of estrogen receptors (ER) α and β as demonstrated by transactivation of estrogen response element (ERE) in cells transiently expressing either ERα or ERβ and by molecular docking of this coumestan into ligand binding pocket of both ERα and ERβ. In breast cancer cells, wedelolactone stimulates growth of estrogen receptor-positive cells, expression of estrogen-responsive genes and activates rapid non-genomic estrogen signalling. All these effects can be inhibited by pretreatment with pure ER antagonist ICI 182,780 and they are not observed in ER-negative breast cancer cells. We conclude that wedelolactone acts as phytoestrogen in breast cancer cells by stimulating ER genomic and non-genomic signalling pathways.

International Clinical Research Center Center for Biological and Cellular Engineering St Anne's University Hospital Pekarska 53 656 91 Brno Czech Republic

Laboratory of Cellular Differentiation Department of Experimental Biology Faculty of Science Masaryk University Kamenice 5 A36 625 00 Brno Czech Republic

Loschmidt Laboratories Department of Experimental Biology and Research Centre for Toxic Compounds in the Environment RECETOX Faculty of Science Masaryk University Kamenice 5 A13 625 00 Brno Czech Republic

Masaryk Memorial Cancer Institute RECAMO Zluty kopec 7 656 53 Brno Czech Republic

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